A thermoplastic resin to be used as a material for the preparation of an electrical or electronic component or a part of an automobile or chemical instrument has been recognized to require high heat resistance. A liquid-crystal polyester resin is one of the resins satisfying this requirement of high heat resistance and is frequently used in the preparation of precision molded articles, because it exhibits low shrinkage when the melt thereof is solidified and is excellent in fluidity. However, even such a liquid-crystal polyester resin is so poor in release characteristics from a mold having a complicated shape that the stable continuous molding thereof is difficult and requires a low molding rate (a long molding cycle), thus resulting in low productivity. That is, although a liquid-crystal polyester resin may be inherently superior in mold release characteristics when compared to other resins, the mold release characteristics thereof are not satisfactory as yet in such molding applications as described above.
Up to this time, addition of a parting agent to a resin has been employed as a means for improving the mold release characteristics of the resin. The following compounds have been known as such parting agents.
(1) addition of a metal salt of a fatty acid, such as zinc stearate or lithium stearate, PA1 (2) addition of a fatty acid ester such as glycerol tristearate, and PA1 (3) addition of a fatty acid amide such as N,N'-alkylenebisalkanamide. PA1 (a) 100 parts by weight of a liquid-crystal polyester resin, and PA1 (b) 0.01 to 5 parts by weight of a fatty acid ester represented by the general formula: ##STR3## wherein at least one of X.sup.1, X.sup.2, X.sup.3 and X.sup.4 is a ##STR4## group and the others are each --H, --OH, an alkyl or an aryl group when not ##STR5## and R is an alkyl or alkenyl group having 2 to 30 carbon atoms. PA1 (1) one or more of aromatic or alicyclic dicarboxylic acids, PA1 (2) one or more of aromatic or alicyclic diols, PA1 (3) one or more of aromatic hydroxy carboxylic acids, PA1 (4) one or more of aromatic thiol carboxylic acids, PA1 (5) one or more of aromatic thiol phenols, and PA1 (6) one or more of aromatic hydroxy amines and aromatic diamines. PA1 (I) polyesters mainly comprising the components (1) and (2), PA1 (II) polyesters mainly comprising the component (3) alone, PA1 (III) polyesters mainly comprising the components (1), (2) and (3), PA1 (IV) polythiol esters mainly comprising the component (4) alone, PA1 (V) polythiol esters mainly comprising the components (1) and (5), PA1 (VI) polythiol esters mainly comprising the components (1), (4) and (5), PA1 (VII) polyester amides mainly comprising the components (1), (3) and (6) and PA1 (VIII) polyester amides mainly comprising the components (1), (2), (3) and (6). PA1 (1) the mold release resistance of the composition of the present invention is reduced to 1/2 to 1/4 of that of a liquid-crystal polyester not containing the fatty acid ester according to the present invention, so that the composition of the present invention can be stably injection-molded in a continuous manner without causing any deformation or breakage of a molded article due to poor mold release characteristics. Thus, the molding cycle of the composition is shortened to remarkably enhance the productivity, and PA1 (2) the parting agent according to the present invention is more stable thermally and chemically than those utilized with liquid-crystal polyesters according to the prior art in injection molding or kneading, so that the composition of the present invention containing the same is less discolored and does not evolve gas during its residence time in an injection molding machine. Therefore, the mold used is not corroded by the decomposition gas. Further, the composition stains to a lesser degree the contact of an electrical component and the mechanical properties of the composition are not adversely affected.
Although the methods (1), (2) and (3) are effective in improving the mold release characteristics of a liquid-crystal polyester resin, they are all problematic in that the parting agent is decomposed to cause discoloration of a molded article, lowering in the mechanical properties thereof and/or gas evolution in kneading or molding, because the thermal decomposition temperature of the parting agent is lower than the molding temperature of a liquid-crystal polyester resin.